Process for preparing perfluoro 3-phenoxypropionic acid

ABSTRACT

Novel compounds of the formula ARE PROVIDED WHEREIN X is -COF, -COCl, -COOH, -COOR, -COOM, CONR1R2, or -CN wherein R is an alkyl radical, M is a metal, and R1 and R2 are independently hydrogen or alkyl radicals. Also provided are novel compounds of the formula C6F5OCF2CF2CF2OCF(CF3)- X wherein X is as defined above. These novel compounds are useful in the preparation of perfluoro(3phenoxypropyl vinyl ether) monomer, said monomer being useful in the preparation of copolymers having improved oxidative stability.

States Patent PROCESS FOR PREPARING PERFLUORO 3-PHENOXYPROPIONIC ACID [72] Inventor: Richard W. Quarles, Jr., Wilmington, Del.

[73] Assignee: E. I. du Pont de Nemours and Comv pany, Wilmington, Del; [22] Filed: March 18, 1970 [21] Appl. No.: 20,806

US. Cl. ..260/521 A, 260/61, 260/465 D, 260/473 G, 260/544 F, 260/544 M, 260/559 B, 260/613 D [51] Int. Cl ..C07c 65/02 [58] Field of Search ..-...260/52l A [56] References Cited UNITED STATES PATENTS 3,192,190 1/1965 Wall et a1. ..260/87.5 3,311,657 3/1967 Graham ..260/539 2,799,712 7/1957 Croix ..260/9l.1 R 2,917,548 12/1959 Dixon ..260/614 F 3,419,610 12/1968 Temple ..260/544 3,467,638 9/1969 Pattisonm, ..260/87.5

[15] 3,694,499 [451 Sept. 26, 1972 Primary ExaminerLorraine A. Weinberger Assistant Examiner-John F. Terapane Attorney-Raymond E. Blomstedt 5 7] ABSTRACT Novel compounds of the formula are provided wherein X is COF, -COC1, .-COOH, COOR, COOM, --CONR R or CN wherein R is an alkyl radical, M is a metal, and R and R are independently hydrogen or alkyl radicals-Also provided are novel compounds of the formula C F OCF CF CF OCF(CF )-X wherein X is as defined above. These novel compounds are useful in the preparation of perfluoro(3-phenoxypropy1 vinyl ether) monomer, said monomer being useful in the preparation of copolymers having improved oxidative stability.

6 Claims, No Drawings perfluorinated monomers PROCESS FOR PREPARING PERFLUORO 3- PHENOXYPROPIONIC ACID BACKGROUND OF THE INVENTION Fluorine-containing copolymers ranging from low molecular weight oils to high molecular weight plastics are of outstanding industrial importance due to their exceptionally good thermal and chemical stability. With the advent of space technology there has arisen a critical need for materials capable of withstanding elevated temperatures in highly oxidative atmospheres. A variety of fluorinated monomers have been developed in an attempt to produce copolymers having the desired resistance to environmental attack. However, the fluorinated monomers of the prior art have not proven entirely satisfactory. For example, attempts to form copolymers of the octafluorovinyl phenyl ether monomer disclosed by Wall and Pummer in U.S. Pat. No. 3,192,190 with other fluorine containing monomers have proven unsuccessful and completely fluorinated copolymers prepared with perfluoroalkyl perfluorovinyl ethers disclosed in U.S. Pat. No. 3,132,123 to Harris and McCane have proven difficult to cure by conventional methods. Thus there is a need for compounds which are useful in the preparation of which are readily copolymerizable with other fluorine-containing monomers and which are cure-site monomers capable of cross-linking wholly perfluorinated copolymers.

THE INVENTION In accordance with this invention, there are provided novel compounds of the formula wherein X is COF, COCI, COOI-I, COOR, COOM, -CONR,R or CN wherein R is an alkyl radical, M is a metal, and R and R are independently hydrogen or alkyl radicals. These compounds are useful in the preparation of a perfluoro(3-phenoxypropyl vinyl ether) monomer and useful polymers prepared therefrom.

The novel compounds above described wherein X is COOM are prepared by heating, in a moisture free inert atmosphere, about 1 mole of a metal salt of pentafluorophenol with about 1-3 moles of tetrafluoroethylene and at least about 1 mole of carbon dioxide in an anhydrous, polar aprotic solvent at 50200C. under autogenous pressurg The corresponding free acid, acid fluoride, acid chloride, ester,

F F l I is prepared by reacting, in a moisture free inert atmosphere, about 1 mole of perfluoro(3-phenoxypropionyl fluoride) with about 1 mole of hexafluoropropylene oxide and pyrolyzing the resulting reaction product at a temperature of about 200-300 C. The reaction between the propionyl fluoride and the hexafluoropropylene oxide is carried out at a temperature of from about C. to about C. in a polar, aprotic, organic solvent. Such polymerizable monomers can, of course, also be prepared by converting the acid fluoride, resulting from the reaction of perfluoro(3-phenoxypropionyl fluoride) with hexafluoropropylene oxide (this acid fluoride and its derivatives, compounds of the formula C F OCF CF CF OEF(CF )-X wherein X is as hereinbefore described, are also novel compounds) to the corresponding carboxylic acid salt and pyrolyzing the acid salt.

The resulting monomer is a superior cure-site monomer in that it can be copolymerized by conventional methods with at least one fluorine containing ethylenically unsaturated comonomer to prepare readily vulcanizable copolymers, vulcanizates of which exhibit exceptionally improved oxidative stability at elevated temperatures. Vulcanizates of such copolymers exhibit excellent heat aged tensile properties, such as tensile strength at break, and retain useful, heat-aged, tensile properties for exceptionally long riqds f me- V. V

Perfluorophenol and its alkali metal salts are known compounds and are described, for example, by Wall et al. in the Journal of Research of the National Bureau of Standards A. Physics and Chemistry, Vol. 67A, pages Hexafluoropropylene oxide is also a known compound and can be made by the action of alkaline hydrogen peroxide on perfluoropropylene at a temp ure fabq fi i V When X is COOM, M is preferably an alkali metal, and most preferably Na, K or Cs.

When X is COOR in the novel compounds of the present invention, R is preferably an alkyl radical of about 1-10 carbon atoms, although it can contain up to 20 carbons.

When X is CONR R R, and R are preferably independently hydrogen of alkyl radicals of about 1-10 carbon atoms, although they can contain up to 20 carbons.

Representative alkyl groups referred to above include methyl, ethyl, propyl, butyl, pentyl, heptyl, nonyl ansqssrl- Preferably the above novel compounds of this invention wherein X is COOM are prepared by heating, in a moisture free closed vessel under a nitrogen atmosphere, about 1 mole of K, Na, or Cs salt of pentafluorophenol with about 2 moles of tetrafluoroethylene and about 4 moles of carbon dioxide in an aprotic polar solvent such as tetraethylene glycol dimethyl either, acetonitrile, dimethyl formamide or dimethyl sulfoxide at about 75150C. for about 2 -12 hours under autogenous pressure.

The other novel compounds, above described, can be prepared from the corresponding metal salts by conventional methods. Detailed descriptions of the preparation of the acid chloride and acid fluoride from the acid salts are given hereinafter.

The perfluoro(3-phenoxypropyl vinyl ether) monomer is prepared from the novel acid fluoride which, of course, can be prepared by conventional methods from the corresponding perfluoro(3-phenoxypropionic acid) and derivatives thereof hereinbefore disclosed In the preparation of the monomer, preferably about 1 mole of the novel acid fluoride is reacted, in a moisture free inert atmosphere, with about 1 mole of hexafluoropropylene oxide in the presence of an anhydrous aprotic, polar, organic solvent such as tetraethylene-glycol dimethyl ether at a temperature of about 2050C. for about 1-3 hours. The lower layer of the resulting product is separated and distilled under reduced pressure. The fraction distilling at about 77-78C. at 11 mm. Hg. is then pyrolyzed to yield the desired monomer.

The pyrolysis is preferably carried out under practically anhydrous conditions at a temperature of about 200300C. The monomer is purified by vacuum distillation and distills at about 84C. at 20 mm. Hg.

A wide variety of comonomers can be copolymerized with the novel monomer of this invention. Useful comonomers include trifluoroethylene, tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene, vinylidene fluoride, 1,1,3,3,3-pentafluoro-l -propene, 1,2,3 ,3,3-pentafluoro- 1-propene, and perfluoroalkyl perfluorovinyl ethers. Perfluorinated comonomers such as tetrafluoroethylene, hexafluoropropylene, and perfluoroalkyl perfluorovinyl ethers containing about 3-8 carbon atoms, as described in US. Pat. No. 3,180,895 to Harris and Mc- Cane, are particularly useful.

A wide variety of conventional copolymerization methods can be employed to prepare such copolymers. Vulcanization of the copolymers can be effected by conventional curing agents such as amine-based curing.

The following examples illustrate the invention. All parts, percentages and proportions are by weight unless otherwise indicated.

All reactions were carried out under a nitrogen atmosphere in such a fashion as to exclude moisture unless noted otherwise.

EXAMPLE 1 Synthesis of C F OCF CF CO Cs One pound (1.4 moles) of Cs CO and 700 ml. tetraethyleneglycol dimethyl ether were placed in a 3- neck 2-liter round bottom flask equipped with a mechanical stirrer, thermometer and dropping funnel and provided with a dry nitrogen atmosphere. To this stirred suspension was added dropwise a solution containing 214 g. (1.16 moles) of C F OH and 200 ml. of tetraethyleneglycol dimethyl ether. After the addition was completed, the reaction mixture was heated to approximately C. for one-ha1f hour, and then cooled to room temperature.

Into a 400 m1. stainless steel shaker tube was placed 200 m1. of this solution. After closing the tube, 40 g. (0.4 mole) tetrafluoroethylene and 50 g. (1.15 mole) carbon dioxide were condensed in. The tube was heated at C. under autogenous pressure for 4 hours. After venting the shaker tube, the solution was drowned in approximately 1,200 ml. of benzene. The resulting precipitate was washed with benzene and air dried. Yield of C F OCF CF CO Cs was 84.5 g. (71 percent, based on the amount of C F 011 taken).

The infra-red spectrum of the salt was consistent with the proposed structure, having a strong absorption at 6.6a, characteristic of the pentafluorophenyl ring, and a carbonyl absorption at 5 .9u, characteristic of the carboxylate salt.

EXAMPLE 2 SyntheSiS Of C3F5OCF2CF2CO2N3.

Into a three-neck 500 ml. round bottom flask, equipped as above, was placed 40 g (377 m moles) Na CO and ml. of tetraethyleneglycol dimethyl ether. To this stirred suspension was added 58.4 g. (3 17 m moles) C F OH dissolved in 100 ml. of tetraethyleneglycol dimethyl ether. After heating to 70C., the odor of phenol was still strong, so 200 ml. H O was added to increase the solubility of the Na CO The solution was heated to reflux overnight.

The bulk of the water was distilled off with the aid of a water pump. The system was then evacuated to the full vacuum of a mechanical pump (ca. 1011.) and approximately one-third of the remaining volume distilled off. The remaining solution was transferred to a 400 cc. stainless steel shaker tube, pressured with 40 g. (909 m moles) CO and 40 g. (400 m moles) TFE and heated to C. under autogenous pressure for 7 hours. After venting the shaker tube, the reaction mixture was drowned in benzene. The precipitate of C F OCF CF CO Na was filtered, washed with benzene and then ether, and dried. The yield was 53 g. (48 percent, based on C F Ol-l The infra-red spectrum of the salt was consistent with the proposed structure, having a strong absorption at 6.6;1., characteristic of the pentafluorophenyl ring, and a carbonyl absorption at 5.9,u, characteristic of the carboxylate salt.

EXAMPLE 3 Synthesis of C F OCF CF CO K Into a three-neck 5round bottom flask, equipped as above, was placed 3 pounds (9.9 moles) K CO and approximately 31 CH CN. To this was added a solution of 1 Kg. (5.44 moles) C F Ol-l dissolved in approximately 1CH CN. The reaction mixture was heated to reflux for 24 hours, cooled to room temperature, and allowed to stand overnight. The solution was decanted from the precipitate and the remaining suspension filtered and then washed with Cl-IBCN. From the solution, 16-200 ml. aliquots were made, plus 21 200 ml. aliquots of wash solution. These 200 ml. aliquots were placed in a 400 ml. stainless steel shaker tube, the tube was pressured with 50 g. (0.5 mole) tetrafluoroethylene and 50 g. (1.15 mole) CO and heated at 100C. for 3% hours. After venting the shaker tube, the cake of product was dried in a vacuum oven at 80C. overnight. The yield from 3 such runs was 308 g., corresponding to an 83 percent yield if the runs from the washings are ignored.

The infra-red spectrum of the salt was consistent with the proposed structure, having a strong absorption at 6.6 1., characteristic of the pentafluorophenyl ring, and a carbonyl absorption at 5.9u, characteristic of the carboxylate salt.

EXAMPLE 4 Synthesis of C F OCF CF COCl Into a 3-neck 1 1 round bottom flask, equipped with mechanical stirrer and reflux condenser, were placed 203 g. (555 m moles) C F OCF CF CO K, 200-300 ml. CH CN, and 35 ml. (58.6 g., 382 m moles) POCl The stirred suspension was heated to reflux overnight. After cooling to room temperature, the mixture was filtered, and the precipitate washed twice with CH CN. The solution and washings were combined an distilled. The fraction boiling at 181C. was C F OCF CF COCI and weighed 153.3 g.

When the filtration apparatus was washed, a second phase, more dense than water, was noticed. It was refluxed overnight with an excess of SOC], and a few drops of pyridine, and yielded a further 21.6 g. of CBF OCF CF COCI. The overall yield was 174.9 g.

( 1 n. 9nt) The infra-red spectrum was consistent with the proposed structure, having the absorption at 6.6g. characteristic of the pentafluorophenyl ring, and a carbonyl absorption at 5.511., characteristic of an acid chloride.

The fluorine nuclear magnetic resonance spectrum was also consistent with the proposed structure.

The synthesis of C F OCF CF COCl can be carried out without actual isolation of the intermediate carboxylate salt. In this case, to the wet cake, from Example 3, is added excess acetonitrile and a slight stoichiometric excess of PCl and the reaction carried out as above.

EXAMPLE Synthesis of C F OCF CF COF One pound of NaF (10.8 moles) and 300 ml. tetramethylene sulfone were placed into a four-neck round bottom flask equipped with dropping funnel, mechanical stirrer, thermometer, an reflux condenser cooled with water. The top of the reflux condenser was connected to a cold finger condenser, cooled with an ice/acetone mixture, on top of a 500 ml two-neck flask immersed in a bath maintained at -80, the second neck on the flask being connected to the vacuum system. Into the dropping funnel was placed 550 g. (1.59 moles) C F OCF CF COCL The pressure was lowered to 3 mm. Hg, the reaction pot heated to between 80C. and 100C. The C F OCF CF COCl was added dropwise. After all of the acid chloride was added, the pot was heated to 120C. to remove all product. The material collected in the receiver was redistilled, B.P. 49C./1 1mm. Hg. The yield of C F OCF CF COF was 441 l g. (84.5 percent based on C F OCF CF COCl).

The infra-red spectrum exhibits the expected pentafluorophenyl absorption at 6.6 and the carbonyl absorption at 53p.

EXAMPLE 6 (187 in moles) C OCF CF CF,OCF(CF )COF, B.P. 77-78/l1 mm. Hg. (39 percent yield, based on 150 g. CaFs EgQEQQL SsQAPL- The infra-red spectrum of C F OCF CF CF O CF(CF )COF exhibited the expected absorptions at 6.6 and 5 .34u.

EXAMPLE 7 Synthesis of C F OCF CF CF OCF==CF The pyrolysis of the. precursor acid fluoride,

using a fluidized bed reactor packed with Na2C which had been dried for 2 days at 300C. under a nitrogen stream.

The bed was maintained at 270300C. and 604 g. (1.21 moles) of C F OCF CF CF OCF(CF )COF was fed by means of a syringe pump at a rate of 1 cc./min. Conversion was practically 100 percent, and a yield of 453.5 g. (89 percent) of C F OCF CF CF OCF==CF obtained (B.P 84l20 mm. Hg).

The infra-red spectrum of the product had absorp tion maxima at 6.6 and 5.49u, the latter being characteristic of a perfluorinated vinyl ether. 9

The fluorine nuclear magnetic resonance spectrum, was consistent with the proposed structure as was the mass spectrum.

I claim:

1, A process for preparing metal salts of perfluoro-3- phenoxypropionic acid which consists essentially of heating, in a moisture free inert atmosphere, about 1 mole of a metal salt of pentafluorophenol with about 1-3 moles of tetrafluoroethylene and at least about 1 mole of carbon dioxide in an anhydrous, polar aprotic solvent at 50200C. under autogenous pressure.

2. The process of claim 1 wherein about 1 mole of a metal salt of pentafluorophenol, about 2 moles of tetrafluoroethylene, and about 4 moles of carbon dioxide are employed.

3. The process of claim 1 wherein the temperature is about -150C.

4. The process of claim 1 wherein the heating is conducted for about 2-12 hours.

5. The process of claim 1 wherein the metal salt is an alkali metal salt.

6. The process of claim 1 wherein the metal salt is a Cs, K, or Na salt. 

2. The process of claim 1 wherein about 1 mole of a metal salt of pentafluorophenol, about 2 moles of tetrafluoroethylene, and about 4 moles of carbon dioxide are employed.
 3. The process of claim 1 wherein the temperature is about 75*-150*C.
 4. The process of claim 1 wherein the heating is conducted for about 2-12 hours.
 5. The process of claim 1 wherein the metal salt is an alkali metal salt.
 6. The process of claim 1 wherein the metal salt is a Cs, K, or Na salt. 